Pulse transmission system



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ATTORNEY Patented July 9, 1946 s PATENT OFFICE.

.PULSE TRANSMISSION SYSTEM ..Nils E. Lindenblad, Port Jefferson, N. Y.,assignor to Radio Corporation of America, a corporation' of DelawareApplication August 13, 1942, Serial No. 454,660

10 Claims.

The present invention relates to a method of and apparatus for producingcarrier wave pulses of short duration.

Oneof the objects of the invention is to en able the production ofsubstantially constant magnitude pulses from stored radio frequencyenergy; J

.A more detailed description of the invention follows in conjunctionwith a drawing, wherein Figs. land .2 illustrate two differentembodiments of the invention.

The same parts are represented by the same reference numerals throughoutthe two figures of the drawing.

Referring to Fig. 1 in more detail, there is shown a pulse typetransmitter in accordance with one embodiment of the invention,comprising an ultra high frequency oscillator O which feeds-into a lowimpedanceline TL of highQ. Line TL is matched to a load, here shown asan antenna comprisinga radiating dipole D in the focus of a parabolicreflector R. Across the line TL at point 'B there is a section ofcoaxial line TL which terminates in a cavity resonator CR, in turnresonant to the frequency of oscillator O. The length of the circuitincluding line section 'I'-L',-as measured from the point 'B to theremote wall of the cavity resonatorlis an odd multiple including unityofa quarter wave at the frequency of oscillator O.

In view of the length'of this quarter wave circuit T'L', CR, it will beseen that when the cavity resonator is excited 'by virtue of the smallamount Y pulse to be generated and radiated. For the sake of energy inline T'L' obtained from line TL, the

cavity resonator will be a high impedance at the end of line T'L' andthus produce a'short-circuit or extremely low impedance across the maintransmission line at the location B. This is the normal condition of thesystem in the absence of any detuning efiects on the resonator.

The line TL acts as a storing device to store up energy fed into it bythe oscillator 0 and has a length equivalent to half the length of spacetravel of the pulse to be transmitted. Such a line, generally speaking,has a large continuous phase distribution or phase angle, and may bemade up of lumped inductances and capacitances, an ordinary coaxialline, or a wave guide. Thus, if it lsdesirEdthat the pulse to beradiated by the antenna be one-tenthof a microsecond duration, 'thel'ineTLsho'uIdbe about fifty feet long electrically; or putting it in otherWords, the line TL has such an electrical length that the time requiredfor a wave to travel thalength of the of compactness, the line TL can becoiled or of the type described in Fig. 1a of my copending application-Serial No. 441,311, filed May 1, 1942. The energy stored up in the lineTL is in the form of a standing wave, the nature of which is that itconsists of'two wave components traveling in upposite directions. Itwill thus be seen that the line system must have such length thatresonance exists during the building up or storage interval.

By means of suitable apparatus such as a gas dischargetube G (havinghelium or argon gas) and an ignition coil switch circuit Efed by .analternating current source S, I am able to detune the cavity resonatorwhenever the spark gap in the tube G breaks down. This detuning of thecavity resonator CR-producedrby a discharge in tube G will change theshort circuit at B to a high impedance, thus permitting the energystored in; .line TL to how into the antenna as a burst of power. Theline TL and resonator CR can thus be looked at as a valve or a quarterwave modulation switch which controls the passage of energy .from themain transmission line TL to the load.

By making the losses in line TL reasonably low, there is obtained aconstant amplitude pulse which has a time duration corresponding totwice the length of line IL from points B to C, for utilization by thantenna. Putting it in other words, there isa substantially uniform flowof energy from line TL to the antenna until all the stored energy inline TL is used up, while the resonator-is detuned. The length of lineTL between points C and B should be a multiple of a half wave.

The interval between pulses, or between times of breakdown of the sparkgap in tube G, should be as large compared to the pulse duration as theoutput power to the antenna'is compared to the oscillator output.

The apparatus at E contains a switch for excit ing an ignition coil andcan have any desired rate of closure. If desired, the switch can beeliminated, and sharp pulses employed to break down the spark-gap in thedischarge tube G.

Fig. 2 is similar to Fig. 1 except that the gas discharge tube of Fig. lis replaced by a'sp'ark gap G. Both of the connections from apparatus Eto the spark gap G" are capacitively coupled 'to there'sonator by meansof metallic plates from a radio frequency standpoint. Such anarrangement constitutes in efiect a blocking condenser for the radiofrequency energy in the resline is substantially one-half the durationof the onator.

, oscillator O can be designed to generate oscillations in theWavelength range of to cm. I'he radiated pulses may be of the order ofone-halfv microsecond or less and repeated at the rate of preferably notmore than 1000 per second.

If desired, the output of oscillator O can be modulated or keyed, inwhich case the pulse rate from the system should be higher than themodulation frequency.

What is claimed is:

1. A pulse transmitter system including a power storing circuit in theform of a radio frequency wave carrying line circuit of large continuousphase distribution, a high frequency oscillator feeding energy into oneend of aid circuit, a load at the other end of said circuit, and meanscoupled across said circuit at a point intermediate the ends of saidcircuit for enabling the energy stored in said circuit to beperiodically utilized by said load, said line circuit having suchparameters that the time it takes a wave to travel the length of theline circuit as measured from the end coupled to the oscillator to saidpoint is equal to one-half th duration of the pulse delivered to saidload.

2. A pulse transmitter including a power storing circuit in the form ofa transmission line, a high frequency oscillator feeding energy into oneend of said line, a load at the other end of said line, a section ofline coupled across said transmission line at a point intermediate theends thereof, a cavity resonator terminating said section at the endremoved from said transmission line, said section and resonator having alength equivalent to one-quarter wavelength at the operating frequenc ofsaid oscillator, a circuit for periodically detuning said resonator foralternately producin low and high impedances across said transmissionline, whereby said section and resonator constitute a quarter wavmodulation switch, said line having such parameters that the time ittakes a wave to travel the length of the transmission line as measuredfrom the end coupled to said oscillator to said point is equal toone-half the duration of the pulse delivered to said load.

3. A pulse type radio transmitter including a power storing circuit inthe form of a low loss transmission line having such parameters that thetime it takes a wave to travel the efiective length of the line is equalto one-half the duration of the pulse to be generated, a source ofcarrierwave energy coupled to said line near one end thereof, an antennacoupled to the other end of said line and matched to said line from animpedance standpoint, and a modulation switch whoselength iselectrically an odd multiple including unity of a quarter wave at thefrequency of said source coupled across said line at a point near saidantenna.

4. A- pulse type radio transmitter including a power storing circuit inthe form of a low loss transmission line havin such parameters that thetime it takes a wave to travel the effective length of the line is equalto one-half the duration of the pulse to be generated, an ultra highfrequency generator of oscillations whose wavelength is of the order ofat least several centimeters coupled to said line near one end, adirective antenna coupled to the other end of said line and matched tosaid line from an impedance standpoint, and. a quarter wave valvecircuit for enabling the periodic utilization of the energy stored insaid line by saidantenna, said quarter wave circuit, includingaresonator coupled by means of a suitable feeder system across said lineat a point intermediate the ends thereof, there being means foperiodically detuning said resonator.

5. A radio, system having a transmitter arranged to store up alternatingcurrent energy and to transmit periodically pulses of stored alternatingcurrent energy 'for time periods short compared to the time intervalsbetween transmitted pulses, said system including an energy storingcircuitin the form of a section of coaxial transmission line having suchparameters that the time it takes a wave to travel the effective lengthof said line is equal to one-half the duration of the pulses generated.

6. A radio system having a transmitter arranged to store up energy andto transmit periodically pulses of stored energy for time periods shortcompared to the time intervals between transmitted pulses, said systemincluding an energy storing circuit in the form of asection of coaxialtransmission line having such parameters that the time it takes a waveto travel the effective length of said line is equal toone-half theduration of the pulses generated, a. source of high frequency energycoupled to said line near one end thereof, an antenna coupled to saidline at the other end thereof and matched thereto, and means coupledacross said-line between said antenna and said source for periodicallyshunting said line with a high and a low impedance for enabling periodicutilization of the energy stored in said line. l l

7. A pulse transmitter in accordancewith claim 1, characterized in thisthat said radio frequency wave carrying circuit of large continuousphase distribution is a two-conductor line.

' 8. A pulse transmitter in accordance with claim 1, characterizedinthis that said radio frequency wave carrying circuit of largecontinuous phase distribution is a wave guide.

9. A radiosystem having a transmitter arranged to store up energy and totransmit periodically pulses of stored energy for time periods short.compared to the time intervals between transmitted pulses, said systemincluding an energ storing'circuit in the form of a line whose effectivelength is such that the time required for a wave to travelthe length ofthe line is substantially equal to one-half the duration of the pulsesgenerated.

10. A radio system having a transmitter arranged tostore up energy andto transmit periodically pulses of stored energy for time periods shortcompared to the time intervals between transmitted pulses, said systemincluding an energy storing circuit in the form of a line whoseeffective length is such that the time required for a wave to travel thelength of the line is substantially equal to one-half the duration ofthe pulses generated, and a load coupled to one end of said line andmatched to said linefrom an impedance t nd NILS E, LINDENBLAD,

